I have a 1982 trans am 305 that I recently acquired, it is crossfire injected and up until yesterday ran pretty good. It came with a carburetor and I installed all the original crossfire equipment on it and finally had it running good but it always had an issue where if I jam the throttle it just chokes and coughs then it goes, but when it goes its fast and fine. But last night out of nowhere it started backfiring out the intake, both throttle bodies, and has a misfire all the time, even at high rpms. If I rev it too quick it actually shoots flames, or a very large puff of gray smoke. While normal driving or revving it sounds like a toy machine gun from the dollar store, it backfires at a constant rate and the only way to make it not backfire while driving is to be as easy on the pedal as possible to keep it going forward, and anywhere above 40mph its at a constant backfire. It misfires as well and I replaced all the plugs with brand new ones and it still does it. I have read that lean issues can cause this and I'm really hoping it's not a valve being stuck open because I was hoping to get this car reliably running for the next few months. It has had a fuel pump replaced some time in the past because there is a big hole cut above the fuel tank so it is very easy to swap in a new pump. I am wondering if anyone has any ideas or has had this problem before. I read about people having an occasional backfire but this is constant and synchronized with the engine's motions. As a test I unplugged the MAP sensor to give it more fuel and it still does it, and I unplugged the CTS and it STILL does it. I am about to try setting the TPS to the proper voltage, but I've tried moving it around and it still does it at any position, and I have also checked the timing and tried all kinds of different settings there, still does it. I also tried unplugged each injector one at a time, still backfires. I tried unplugging the fuel pump just to make sure its working and the instant I unplugged the wire it shut the engine off. I know the plug wires are all going to the right spots, ive checked that a dozen times as I changed the plugs twice since I put on the crossfire because I had a rich issue that turned out to be the CTS. The cap and rotor are brand new too. I am completely stumped! HELP PLEASE!!

 

Have you done a swap from something? A MAP sensor on an 82 is kinda....odd. Maybe I am wrong, but I dont think it had a MAP sensor with cross-fire. It sounds like you may have put in your distributor off a tooth or two or your timing chain may have jumped a tooth. If you think it could be a stuck valve, start pulling the valve covers and crank it over. But it sounds to me like definatly a timing issue.

 

It does have a MAP sensor from stock, I even got the vacuum diagrams from my school's library and it shows where the sensor plugs into the master throttle body. Without it the fuel flows really fast and it fouls the plugs. I put the distributor in the same way it came out, I noted where it was when it came out and like I said it has been running good for a couple days then I just went out to drive it one night and bam it had no power and was doing all this and has been like this since. The TPS is at the right voltage now, I tried unplugging both IACs, still no go. I really hope the timing chain didn't jump how involved is that? I wouldn't know how this would have happened, is this known to happen out of nowhere? The motor has 60000 miles on it and runs amazing when tuned correctly. Can this sort of thing happen with both cam timing and spark timing?
Also, will the engine even run if the cam timing was off a tooth? I messed up the cam timing on my van and it barely started and if it did it was so bad it died very quickly

 

we should just take a vote:

ignition coil or other part on the distributer?
fuel filter (unknown condition)
fuel pump (maybe underpowered?)
valve not closing?

Is unplugging the CTS or MAP to make more fuel pour in a viable test? Because I did that and it still backfired just as bad
The way it happened just out of nowhere with no warning just makes me think a part failed, thanks for the reply so far!

 

In order: Check fuel pressure, ignition timing, vacuum leaks (which CFI is notorious for having), and cam timing. Ive had quite a few LU5 cars and theyre not that hard to set up, but it sounds like you have a problem that stems past the induction setup.

 

well I have to change the valve cover gaskets anyway, and I already have the gaskets to go on so itll be my excuse to see if the valves are all moving in and out. I'll adjust them too and see if that helps. I'll post back with results.

 

Adjust them with the engine running. You get the best results that way.

 

oh of course, I didn't know it could be done otherwise


I should add that the backfire happens even on a completely cold engine, and it also does not let up as the rpms get higher, most of the time if it gets too high the backfire gets so huge that it explodes and stops the engine immediately. However it can start right back up again.

 

still havent done the valve cover yet, i tried unplugging each plug one by one and it still backfires, and then i started to remove them one by one and leave them off, i had it down to running (yes running) on 2 cylinders, and it STILL backfires, this eliminates any valve problems right?

 

Ok I took off the distributer cap and found the rotor actually was flopping around and one screw wasn't even holding it in. However, after I took it out and inspected it and put it back in tight, it still backfires. Could the rotor be messed up from flopping around? Is the tip that runs past the spark plug posts supposed to be flat or slightly rounded?



Edit: The engine WILL run high revs, up to 5000rpm without backfire, but you gotta go slowly, if you hit the throttle too fast it backfires. Rah this is getting really frustrating, and embarassing

 

ok it was what i feared the most


the pushrod for one of the valves on cylinder 4 isnt opening the valve more than a milimeter at best, i took out both pushrods for that cylinder and the backfire went away
funny thing is, i can unplug that spark plug and it still backfires, but maybe its just shooting the gas mixture back out by compression alone?

I dont know but this sucks, either i need a new cam or there is a lifter problem either way the intake has to come off AGAIN

thanks for everyone who helped though!

any recommendations on what i should do for a cam replacement? anything "cool" i can get since i have to anyway? I dont plan to get new heads, or new anything except maybe exhaust somewhere down the road but i basically just want this to be a daily driver not a performance beast, its fast enough as stock.

 

what is the chance that the 13mm socket and extension i still havent found since i did the intake manifold gaskets might be stuck somewhere underneath the manifold?

 

so I finally got around to working on it again, so far within an hour (had to leave for work) I got the two lifters out from that cylinder, and one is concave and shaped like a crater on top and the other is flat and perfect. What are the chances that just the lifter got wore down and the camshaft is alright? I felt down there with my finger but could only feel a little and can't really see down there from any angle. Are lifters known to wear down without the camshaft wearing down?

 

EXACTLY zero. Not even one in a billion.

It's cam time. Wouldn't be a bad idea though, to first figure out why it rolled off that one lobe. Sometimes it's just luck of the draw; but it can also be inadequate or improperly installed valve springs, or improper installation, or incorrect lubrication.

It is ALMOST CERtAINLY NOT the cam mfr. That is, it DID NOT happen just because it's a Comp, or Lunati, or Crane, or whoever else you see people bashing on the various car forums. It's everybody. It's a sign of the times I guess, and the times are, time to change to a roller. It has to do mostly with motor oil formulation, and the fact that virtually all automotive motor oil no longer has the zinc and other metallic compunds in it that used to provide the right kind of lube for flat-tappet cams.

Meanwhile, there's a very large chance that the metal that was shed off that lobe and lifter, has got into bearings and everything else; and even if you successfully install another cam, the motor may already be destroyed even though it appears OK now. It may need to be torn down and have a rifle brush run through every oil passage at the quarter car wash, and of course new rings and bearings at re-assembly.

 

It's possible! I have made that mistake once! It wasn't a motor for a real car though. Just when I was at UTI and I was in Hot Rod class. We put an intake on, slapped the motor in a t-bucket and dynoed it. It sure sounded funny! Since we tore most of the motor apart after each pull we found it pretty quick, and had a good laugh. The instructor never found out about it.

Sounds like you've already figured out your problem though.

 

It better not be as horrible as you say it is, or I'm selling it, I am not dealing with another unreliable car that needs a bunch of work, if it runs and it has any problems like that I will sell it as is. Can I just go to an autozone or murray's and just buy roller lifters and a cam? I just bought a 3.99 lifter to replace the bad one and I was going to get the cam as soon as I find out the condition of this one. I thought this car was going to be a great deal when I bought it, this only happened after I fixed everything else in it

I am going over to work on it now again for the first time in a couple days, I am hoping it isn't so bad

 

Yeah the lobe is wiped, I started to take stuff apart then I just got discouraged and went home after a half hour of working, I am getting quite tired of car work for this year

Who wants to buy a 1982 trans am all original in South Eastern Michigan? I will gladly trade for any running v8 t-topped f-body car. rah

 

I'd love to find a car like yours in my area. I'd put my 383 in there.
Look at the bright side. It still runs and you can drive it til you get a new shortblock, and it's only a 305 that you're losing anyhow.
Doors are being opened for you to have a genuine fast car. Isn't that what you wanted to begin with? Don't be bummed, you're getting your wish.

 

I appreciate the consoling words, It's just lately I've gone through quite a few cars, that all had problem after problem after problem, and I had high hopes for an f-body, my old camaro had NEVER failed me or had any problems like this, and i beat on that thing all day long. I've been doing car work nearly every day now for the past year. I'm going to fix it if I don't get any offers on it, I already listed it in the classifieds and on craigslist. I'de rather have a camaro anyway

 

I REALLY feel u man.

I did pretty much similar job, intake mani gaskets and lifter job.
I'm missing the distributor hold down clamp, I bought a new one and used that for reassembly but Im scared to death I dropped that into the chamber too, or the dist. hole..

caz my cars misfiring and almost sounds like a knock too
but i heard a misfire sounds really loud too so Im hoping for the best.. but being ready for the worst..

 

a misfire for me has always sounded just like the engine just spins freely for one ignition, which doesnt ignite. The car will shake more, very noticably more, and sound like a machine gun rather than a vacuum cleaner. can the distributer hold down clamp even fit in the hole? the way I see it if that piece fell into the hole and made the car misfire, you'd know it lol, it would probably bust something violently and freeze up the engine or something. I once dropped a socket in my ranger's engine bay behind the engine, and while feeling for it noticed the transmission has a roughly 1"x1" square opening in the bellhousing, and I was scared to death it would get stuck in my clutch or something, but I never found that socket, and never found any abnormal problems with it. and I STILL CANT FIND MY 13MM SOCKET AND EXTENSION

they probably fell inside of the bumper and got lost on the road when I took it for a test drive.